Accelerator of vulcanization



Patented Dec. 21, 1937 UNITED STAT S.

2. 2 ACCELERATOR F v cnNIzA'non 1 Rcbert C, Goodwin Lubbock, Tjex., and Arthur Sloan, Akron, Ohio; said Sloanassignor to The B. F. Goodrich company; New York, N. Y., a corporation of New York. p

V Dr wing," Application April 11, 1936,

; g; 1 Serial No. 113,969 1 1 leciaims. (c1. 1s 53) I p p carbamateyand finally converting :it to the de This invention relates to the art of rubber manufacture and has as its chief object to provide anew and improved class of accelerators of vulcanization. This application is a continuation in part of our copending application Serial No.

704,292 filed December 28, 1933.

Derivatives of dithiocarbamic acids were among the first known organic accelerators of vulcanization. The salts of dialkyl dithiocarbamic acids are very readily prepared by the simple reaction of carbon disulphide with the appropriate dialkyl amine, but have never been widely used because of their high cost, relative instability, and their extreme activity at the temperatures at which l5 rubber is ordinarily processed, which results in a pronounced tendency to prevulcanization. Similar derivatives of mono-aryl and alkyl-aryl dithiocarbamic acids have been proposed as accelerators, but they too are somewhat unstable .20 and exhibit no marked advantages over other more readily prepared accelerators, hence have not been widely used.

In theprocess of this invention the vulcanization of rubber is accelerated by diaryl dithiocar- 25 bamates of bivalent metals. For example, the

salts of diphenyl dithiocarbamic acid or the similar ditolyl (ortho, meta, para or mixed), dinaphthyl (alpha, beta or mixed), phenyl-naphthyl, phenyl-cumyl or other like diaryl substituted 30 dithiocarbamic acids with magnesium, zinc, cadmium, lead, tin (stannous) or other like bivalent metals are all excellent accelerators of vulcanization. The properties of these salts, in which the metal is combined solely with diaryl substituted 35 dithiocarbamic acids, differ markedly from those of salts of aliphatic substituted acids, and in particular are practically free from any tendency to prevulcanize rubber or cause scorching although they bring about a rapid vulcanization at ordinary vulcanizing temperatures. The individual members of this class vary in activity over a considerable range, the lead salts generally being rather slow accelerators and the zinc salts quite rapid, although the order of activity of the 5 various salts of the different acids is not always the same. Thus the zinc salt of phenyl betanaphthyl dithiocarbamic acid is a stronger accelerator than the lead salt, whereas the reverse is true of the salts of phenyl alpha-naphthyl dithio- 5 carbamic acid. These salts cannot be prepared directly from carbon disulphide and the diarylamine, as can the aliphatic compounds, but are readily prepared by first replacing the hydrogen of the diarylamine by an alkali metal, then add- 55 ing carbon disulphide to form the alkali dithioress.

sired bivalent metal salt by double decomposition with a soluble salt of the desired metal. 7

As a specific example of one embodiment of the method of this invention, a rubber composi- 5 tion is prepared by mixing 100 parts by weight of rubber, 5 parts of zinc oxide, 1 part of stearic acid, 3 parts of sulphur and 0.5 part of zinc diphenyl-dithiocarbamate. The mixture is vulcanized by heating for 20 minutes at 275 F. in a 10 The product is strong and well vulcanized. Somewhat better results are obtained by adding a nitrogenous base to activate the accelerator. For example, when 0.3 partof zinc diphenyldithiocarbamate are used as accelerator in the above composition along with 0.2 part of polybutylidene-aniline as an activator, the mixture when vulcanized under the same conditions is considerably stronger and stiffer.

It is to be understood that the specific example given above is merely illustrative of one manner of use of the accelerators of this invention, that other accelerators within the scope of the class herein defined may be substituted for the specific compound used in the example, and that the ac- 'celerators of this invention may be used in admixture with each other or other known accelerators, or with age-resistors, organic acids, amines, softeners, pigments, fillers, etc. and that the rubber may be vulcanized with the assistance of this new class of accelerators in other manners than that particularly set forth above; specifically, it may be vulcanized in hot air, steam, hot water, etc. The term aryl as herein employed refers to univalent aromatic hydrocarbon radicals whose free valence belongs to the nucleus and not to a side chain.

The scope of this invention is accordingly not to be limited to the specific examples herein set forth, but is to be limited only as required by the 40 prior art and as indicated in the appended claims.

We claim:

1. The process which comprises vulcanizing rubber in the presence of a salt consisting of a bivalent metal combined solely with diaryl dithiocarbamic acids.

2. The process which comprises vulcanizing rubber in the presence of a salt consisting of zinc combined solely with diaryl dithiocarbamic acids. 5

3. The process which comprises vulcanizing rubber in the presence of zinc diphenyl-dithiocarbamate.

4. The process which comprises vulcanizing rubber in the presence of a salt consisting of a 65 a bivalent metal combined solely with diaryl dithiocarbamic acids.

9. The process which comprises heating a mixture of rubber, sulphur, a nitrogenous base, and a salt consisting of a bivalent metal combined solely with diaryl dithiocarbamic acids.

10. The process which comprises heating a mixture of rubber, sulphur, a nitrogenous base, and a salt consistingof zinc combined solely with diaryl dithiocarbamic acids.

11. A rubber composition which has been vulcanized in the presence of a salt consisting of a bivalent metal combined solely with diaryl dithiocarbamic acids.

12. A rubber composition which has been vulcanized in the presence of a salt consisting of zinc combined solely with diaryl dithiocarbamic acids.

13. A rubber composition which has been vulcanized in the presence of zinc diphenyl-dithiocarbamate.

14. A rubber composition which has been vulcanized in the presence of a salt consisting of a bivalent metal combined solely with a phenyl naphthyl dithiocarbamic acid.

15. A rubber composition which has been vulcanized in the presence of zinc phenyl betanaphthyl dithiocarbamate.

16. A rubber composition which has been vulcanized in the presence of lead naphthyl dithiocarbamate.

ROBERT C. GOODWIN. ARTHUR W. SLOAN.

phenyl alpha- 20 

